We present the case of a 70-year-old woman who was admitted to our hospital with heart failure due to a giant left ventricular aneurysm involving the apex and severe mitral regurgitation. Three months before the hospitalization, percutaneous coronary intervention was performed for severe stenosis of the left main trunk. During the procedure, there were no abnormalities of distal coronary flow due to problems like embolization, and repeat coronary angiography, performed after stabilization of heart failure, showed no new significant stenosis. We diagnosed her condition as a subepicardial aneurysm by pathological examination of the resected specimen.